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In organic chemistry and biochemistry, important examples include amino acids and derivatives of citric acid. Although an amphiprotic species must be amphoteric, the converse is not true. For example, a metal oxide such as zinc oxide, ZnO, contains no hydrogen and so cannot donate a proton. Nevertheless, it can act as an acid by reacting with ...
The reaction occurs in the light reactions in all photosynthetic organisms. A few organisms, including the alga Chlamydomonas reinhardtii and cyanobacteria , have evolved a second step in the dark reactions in which protons and electrons are reduced to form H 2 gas by specialized hydrogenases in the chloroplast .
Biological hydrogen production is also observed in nitrogen-fixing cyanobacteria. This microorganisms can grow forming filaments. This microorganisms can grow forming filaments. Under nitrogen-limited conditions some cells can specialize and form heterocysts , which ensures an anaerobic intracellular space to ease N 2 fixation by the ...
Important reactions that result in hydrogen production start with glucose, which is converted to acetic acid: [1] C 6 H 12 O 6 + 2 H 2 O → 2 CH 3 CO 2 H + 2 CO 2 + 4 H 2. A related reaction gives formate instead of carbon dioxide: C 6 H 12 O 6 + 2 H 2 O → 2 CH 3 CO 2 H + 2 HCO 2 H + 2 H 2. These reactions are exergonic by 216 and 209 kcal ...
Water is amphoteric, meaning that it can exhibit properties of an acid or a base, depending on the pH of the solution that it is in; it readily produces both H + and OH − ions. [c] Related to its amphoteric character, it undergoes self-ionization. The product of the activities, or approximately, the concentrations of H + and OH −
By some definitions, "organic" compounds are only required to contain carbon. However, most of them also contain hydrogen, and because it is the carbon-hydrogen bond that gives this class of compounds most of its particular chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry. [ 12 ]
Many organic compounds also contain H atoms, such as hydrocarbons and organic matter. Given the ubiquity of hydrogen atoms in inorganic and organic chemical compounds, the hydrogen cycle is focused on molecular hydrogen, H 2. As a consequence of microbial metabolisms or naturally occurring rock-water interactions, hydrogen gas can be created.
The inverse recombination reaction H 3 O + + OH − → 2 H 2 O. is among the fastest chemical reactions known, with a reaction rate constant of 1.3 × 10 11 M −1 s −1 at room temperature. Such a rapid rate is characteristic of a diffusion-controlled reaction, in which the rate is limited by the speed of molecular diffusion. [15]